Yeah that's a pretty bad drop. Oil definitely thins out with heat, but that 10296 pump should keep up even with big bearing clearances and thinner oil. My 417" LS3 has 10296, .0030 main clearances, .0025 rods clearances, Holley 302-3 pan, 10-30 oil. Cold idle pressure is 45-50psi, hot idle (like 250deg oil temp) is 26-29psi. At temperature it cruises in the mid 40s for pressure and goes high 60s under throttle. I think you've got an unexpected leak path in there somewhere if you're in the teens for oil pressure.